Two years ago, state Senator Ken LaValle didn’t know the name of his election opponent until late August.

This year he’ll have to wait a month longer than that.

Meeting last week, the Suffolk Democrats did not select either of the women seeking to take on the veteran Republican, now in his 36th year. Instead, the party cleared the way for the two, Southampton Councilwoman Bridget Fleming and Rocky Point attorney Jennifer Maertz, to fight it out in a Sept. 13 primary.

The Democrats also chose Mattituck resident Nicholas Deegan, a local parks district commissioner who ran unsuccessfully for a seat on the Southold Town Board last fall, to oppose GOP Assemblyman Dan Losquadro of Shoreham.

The party would have preferred to avoid the Senate primary, but neither candidate would withdraw, said Suffolk Democratic leader Rich Shaffer.

“I said to both of them can they try to figure it out,” Mr. Shaffer said. “They won’t have a lot of time to take on someone who’s been around forever, but neither one wanted to back out. Since they’ve both been important parts of our committee we’ll let Democratic voters make the decision.”

The First Senatorial District covers most of Brookhaven and all five East End towns.

Each candidate must obtain 1,000 petition signatures from registered Democrats by July 12 to secure a spot in the primary.

The race in 2010 appeared to be between Mr. LaValle, who was first elected in 1976, and New Suffolk attorney Regina Calcaterra.

But Ms. Calcaterra was thrown off the ballot after two state courts said she didn’t meet the state’s residence requirement. Ms. Maertz, who served as her campaign chief of staff, ran in her place but lost to Mr. LaValle.

Ms. Calcaterra now serves as chief deputy to Suffolk County Executive Steve Bellone.

Ms. Fleming gained a Southampton Town Board seat by winning a special election in 2010. She ran again last fall and won a full four-year term.

In the First Assembly District contest, Mr. Deegan will attempt to deny the GOP incumbent a second term.

Mr. Losquadro won his first term by beating Democrat Marc Alessi in a very close race. On Election Night 2010, Mr. Losquadro, then a county legislator, had a lead of just 40 votes over the three-term incumbent. The race ended three weeks later, when after a recount the Republican’s lead stretched to over 800 votes.

Mr. Deegan, a carpenter, currently serves as one of three Mattituck Parks District commissioners.

He’s been active on the Southold Town parks and recreation committee and has coached soccer and baseball for 14 years. During last year’s election he described himself as a fiscal conservative, the result of owning a small business for 25 years.

Mr. Deegan “has a tough row to hoe,” Mr. Shaffer said. “But he’s obviously concerned with the community. He’s a trouper and a true believer that we need to have competition in these races.”

With most of the Assembly district within Brookhaven Town and with the GOP holding a considerable edge in voter enrollment, Mr. Deegan said he’s under no illusion that his will be anything but an uphill campaign.

“I’d like to represent the North Fork as part of the majority in Albany,” he said. “I’d be able to bring more resources back to the neighborhood and be part of Governor Cuomo’s effort to bring more efficiency in government.”

Southold Democratic leader Art Tillman said Mr. Deegan has distinguished himself as a reformer during his tenure as a parks commissioner, including ending the years-running abuse of gasoline cards by commissioners.

“When Nick Deegan is elected he will bring to Albany the same work and reformist ethic he has demonstrated here in Mattituck,” said Mr. Tillman.

The selection of congressional candidates had also taken place in the spring, but given the state’s decision to set a separate, much earlier congressional primary date — this year on June 26 rather than September — both parties made their selections two months earlier in March.

As expected, Democrats renominated incumbent Rep. Tim Bishop, who is seeking his sixth term. With GOP candidate George Demos dropping out at the last minute, there will be no GOP primary. The nomination went to businessman Randy Altschuler, who lost to Mr. Bishop in 2010 in one of nation’s closest congressional contests.